1. Field of the Invention
The present invention relates to an anti-reflection coating with a low resistivity function and a transparent conductive coating which can be used as an as outermost layer. In particular, this invention relates to a multi-layer system that has a high anti-reflection effect.
2. Description of the Related Art
An anti-reflection multi-layer system is usually used as a plastic substrate, a glass substrate, or a plastic web. A great number of multi-layer systems have previously been disclosed.
U.S. Pat. No. 4,921,760 discloses a multi-layer anti-reflection coating with excellent adhesion between the CeO2 layer and the synthetic resin. The layer system includes CeO2, Al2O3, ZrO2, SiO2, TiO2, and Ta2O5. All the thin films of the layer system are oxide materials. There are 3 to 5 thin layers in the layer system. For example, the total thickness of the 5-layered structure is about 3580 angstroms. The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,105,310 discloses a multi-layered anti-reflection coating designed for in-line coating matched with reactive sputtering. The layered system includes TiO2, SiO2, ZnO, ZrO2, and Ta2O5. All the thin films of the layered system are oxide materials. There are 4 to 6 thin layers in the layer system. For example, the total thickness of the 6-layered structure is about 4700 angstroms. The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. Nos. 5,091,244 and 5,407,733 discloses a new type of electric conductive light-attenuating anti-reflection coating. The major claim is an article comprising of nitrides of a certain transition metal that provides an electrically conductive, light-attenuating, anti-reflection surface. The layer system includes TiN, NbN, SnO2, SiO2, Al2O3, and Nb2O5. The thin films of the layer system are nitride and oxide materials. There are 3 to 4 thin layers in the layer system. For example, the total thickness of the 4-layer structure is about 1610 angstroms. The transmission of visible light through these two-layer systems is less than 50%. The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,147,125 discloses a multi-layered, anti-reflection coating using zinc oxide that provides shielding from UV wavelengths shorter than 380 nm. The layered system includes TiO2, SiO2, ZnO, and MgF2. All the thin films of the layered system are made of oxide or fluorine. There are 4 to 6 thin layers in the layer system. For example, the total thickness of the 5-layer structure is about 7350 angstroms. The material of the surface layer of the layer system is MgF2, which scores low on the refractive index at about 1.38 at 550 nm.
U.S. Pat. No. 5,170,291 discloses a 4-layer system, which is optically effective and has a high anti-reflective effect. The layers can be formed via a pyrolytic method, a plasma-supported chemical vapor deposition method, a sputtering method, or a chemical deposition method. The layered system includes SiO2, TiO2, Al2O3, ZnS, MgO, and Bi2O3. For example, the total thickness of the 4-layered structure is about 2480 angstroms. The material of the surface layer of the layered system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,216,542 discloses a 5-layered coating with a high anti-reflection effect. The process uses an adhesive layer of Ni, Cr, or NiCr metal with a thickness of about 1 nm (nanometer). The other four layers are composed of SnO2, ZrO2, ZnO, Ta2O5, NiO, CrO2, TiO2, Sb2O3, In2O3, Al2O3, SiO2, TiN, and ZrN. For example, the total thickness of the 5-layered structure is about 2337 angstroms. The transmission of visible light through this layered system is less than 30%. The material of the surface layer of the layered system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,541,770 discloses a light attenuating anti-reflection coating including electrically conductive layers. It is a four or five-layer system. A light absorption high refractive index metal such as Cr, Mo, or W is used as an optically effective thin film in the layer system. The other three or four layers are TiO2, ITO, Al2O3, SiO2, or TiN. The patent discloses that the major materials of the layer system are oxide and nitride, and only one metal film is used as an optically effective thin film in the anti-reflection coating. For example, the total thickness of the 5-layer structure is about 1495 angstroms. The transmission of visible light through this layer system is less than 60%. The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,362,552 discloses a 6-layer anti-reflection coating including three layers of an electrically conductive metal oxide. The layer system includes SiO2, ITO, Nb2O5, and Ta2O5. A total optical thickness of up to about one-wavelength of visible light of the electrically conductive metal oxide may be included in the coating. As an example of the 6-layer structure, the materials and thickness of the major two layers within this 6-layer system are SiO2 (854 angstroms), and ITO (1975 angstroms). Moreover, the material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. No. 5,579,162 discloses a 4-layer anti-reflection coating for a temperature sensitive substrate such as plastic. One layer is a DC reactively sputtered metal oxide that may be deposited quickly and without imparting a large amount of heat to the substrate. The layer system includes SnO2, SiO2, and ITO. For an example of the 4-layered structure, the materials and thickness of the major two layers within this system are SnO2 (763 angstroms), and SiO2 (940 angstroms). The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
U.S. Pat. Nos. 5,728,456 and 5,783,049 disclose an improved way to deposit anti-reflection coating on plastic film. The multi-layer thin film is coated via a roller coating with a sputtering process. The layer system includes ITO, SiO2, and a thin lubricating covering layer that is a solvent-soluble fluoropolymer. For example, the total thickness of the 6-layer system is about 2630 angstrom. The material of the surface layer of the layer system is SiO2, which scores low on the refractive index at about 1.46 at 550 nm.
The above descriptions show clearly that the materials of the thin surface layer of the conventional optical layer system are SiO2 or MgF2, which score low on the refractive index at about 1.46 and 1.38 at 550 nm, respectively.
It is well known that the conventional layer structure for an anti-reflection optical coating has a general principle. This general principle is that the surface layer of the optical coating should be a material that scores low on the refractive index such as SiO2, scoring 1.46 on the refractive index, or MgF2, scoring 1.38 on the refractive index. However, when we apply the anti-reflection coating on a display screen to create an anti-static effect for a computer monitor, or low reflection glass for an LCD or a PDP, there are some bottlenecks in the process for high volume mass production. The basic reason for this is that in the conventional optical layer structure the conductive layer is buried by an insulating layer, for example SiO2 or MgF2.
In the general design rule for an anti-reflection coating, the first layer deposited on the substrate surface is a material with a high score on the refractive index (hereafter referred to as H), which is then followed by a second layer which is a material with a low score on the refractive index (hereafter referred to as L). The basic design rule for the conventional anti-reflection coating is that there is a layer structure such as HLHL or HL HL HL. In a simple case, if the materials of H are ITO and the materials of L are SiO2, the 4-layered structure is glass/ITO/SiO2/ITO/SiO2. Because ITO is a transparent conductive material, the multi-layer coating of this layer structure has electrical conductivity of less than 100 Ω/square, and can be used as an EMI shielding and/or electric static discharge when the conductive coating layer is bonded to the ground. However, a troubling phenomenon is that if the surface material of the conventional optical layer structure is SiO2, the typical thickness of the SiO2 layer is about 1000 Å. The material characteristic of SiO2 is that it has a high density, inert properties in chemicals and is a very good insulating layer for electricity. In the process of applying a conventional anti-reflection coating to a display screen, it is difficult to make an electrical contact with the buried ITO layer that is isolated by the outermost SiO2 layer. For a typical grounding process to make a metal contact with the ITO layer, an ultra-sonic welding procedure is needed to break the insulating layer (SiO2) and to make sure a good contact of tin solder is made with the buried ITO conductive layer. This process slows down the application of anti-reflection coating in high volume production.
Alternatively, an ultra-sonic welding process produces small and bright contamination because of the liquid tin, and the explosive energy of the ultra-sonic process. This process also produces inconsistent contact resistance for each bus bar line because the ultrasonic-welding process cannot consistently break the insulating coating at the same depth evenly and obtain a uniform contact resistance with the ITO layer.
The drawbacks mention above will reduce the yield and reliability of the manufacturing process for the application of conventional anti-EMI and anti-reflection coating.